This invention relates to a method for damping underwater sound caused by a marine vessel and to a marine vessel equipped with apparatus to damp underwater sound.
When carrying out seismic measurements at sea, floating acoustic measuring devices are towed by a marine vessel. However, the noise caused by the towing vessel may badly disturb the function of the measuring devices. To avoid this, it is necessary to take action either to damp the noise caused by the vessel towing the measuring devices or to divert the noise to the sides, so that it cannot disturb the measurement operation.
It is known from U.S. Pat. No. 3,084,651 to use a water bubble zone to damp sound spreading in water and/or to change its propagation direction. In this prior art specification it is stated that earlier attempts to use an air bubble zone for the above mentioned purpose have failed because the air bubbles formed have been too large and have joined together to form still larger bubbles, which too rapidly rise to the water surface. According to the teachings of U.S. Pat. No. 3,084,651, air should be mixed into a liquid flow in a pipe, so that a water/air mixture is formed which can be injected into the water surrounding the vessel. However, this method is difficult to apply, because it requires water and air mixing tubes to be provided externally of the vessel.
The object of the present invention is to solve, in a more simple manner, the problems related to the forming of an air or gas bubble zone, so that bubbles of suitable size as well as a bubble zone of a suitable shape is achieved without complicated accessories.